Passive rf tag with power cycling

ABSTRACT

A passive tag embedded in a package includes multiple conductive coils. A first coil receives radio frequency (RF) energy used to power the tag. Additional coils receive and/or transmit data signals, clock signals, and carrier signals. The RF energy and other signals may be at different frequencies. An RF probe includes a first coil to emit the RF energy to power the tag. The RF probe includes additional coils corresponding to the additional coils in the tag. The RF probe may turn off the RF signal used for power during communication. The RF energy may be rectified to provide DC power to circuits in the tag, or may be used directly for adiabatic circuits. The RF probe and the package may have complementary shapes to facilitate alignment of the coils.

FIELD

The present invention relates generally to passive radio frequency (RF)tags, and more specifically to communications with passive RF tags.

BACKGROUND

Passive RF tags are used for many purposes, such as inventory controland records tracking. Passive RF tags include a conductive coil that isused to scavenge energy from an interrogating RF field. Theinterrogating RF field and the conductive coil are also used for datacommunications. Interrogating RF fields are typically at 13.56 MHz, andconductive coils are typically a few centimeters in diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a system including a radio frequency (RF) probe and apassive tag;

FIG. 2 shows a top view and section view of a package that includes apassive tag;

FIG. 3 shows a tip of an RF probe and a passive RF tag;

FIG. 4 shows the tip of an RF probe and a passive RF tag, both withthree conductive coils affixed thereto;

FIG. 5 shows the tip of an RF probe and a passive RF tag, both with fourconductive coils affixed thereto;

FIG. 6 shows a package with a notched indentation and a matching RFprobe;

FIG. 7 shows a package with a trapezoidal indentation and a matching RFprobe;

FIG. 8 shows a block diagram of a passive tag;

FIGS. 9-13 show block diagrams of RF sections of passive tags inaccordance with various embodiments of the present invention;

FIG. 14 shows a block diagram of a passive RF tag with adiabaticcircuits; and

FIGS. 15-17 show flowcharts of methods in accordance with variousembodiments of the present invention.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, variousembodiments of an invention. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention. It is to be understood that the various embodiments of theinvention, although different, are not necessarily mutually exclusive.For example, a particular feature, structure, or characteristicdescribed in connection with one embodiment may be implemented withinother embodiments without departing from the scope of the invention. Inaddition, it is to be understood that the location or arrangement ofindividual elements within each disclosed embodiment may be modifiedwithout departing from the scope of the invention. The followingdetailed description is, therefore, not to be taken in a limiting sense,and the scope of the present invention is defined only by the appendedclaims, appropriately interpreted, along with the full range ofequivalents to which the claims are entitled. In the drawings, likenumerals refer to the same or similar functionality throughout theseveral views.

FIG. 1 shows a system including a radio frequency (RF) probe and apassive tag. System 100 includes computer 110, RF probe 120, package130, and passive tag 140. In embodiments represented by FIG. 1, passivetag 140 is affixed to package 130 in a tamper-proof manner. For example,passive tag 140 may be embedded in an indentation 132 of the package ina manner that causes the tag to be destroyed if attempts are made toremove it.

In operation, RF probe 120 emits an RF signal used to power passive tag140. Passive tag 140 receives the RF signal and scavenges enough energyto operate circuitry in the tag. When the tag has enough power tooperate, data communications can take place between RF probe 120 andpassive tag 140. Computer 110 is in communication with RF probe 120, andcan perform any suitable data processing tasks. For example, in someembodiments, computer 110 performs identity verification of passive tag140.

As described further below, passive tag 140 includes multiple conductivecoils used for different purposes. One of the conductive coils is usedto scavenge power from an RF signal transmitted by the RF coil. Othercoils are used in various combinations for one or more of receiving andtransmitting data, receiving a clock signal, and receiving a carriersignal.

RF probe 120 also includes multiple conductive coils used for differentpurposes. For example, one of the conductive coils is used to emit RFenergy to power passive tag 140. Other coils are used in variouscombinations for one or more of receiving and transmitting data,transmitting a clock signal, and transmitting a carrier signal.

In some embodiments, each of the multiple conductive coils in passivetag 140 correspond to a respective coil in RF probe 120, and the coilsare placed in close proximity to each other to effect communications.Various embodiments of the present invention include mechanisms toensure alignment of the RF probe and the tag, thereby ensuring alignmentof the coils to effect communications.

In some embodiments, power transfer occurs at a first frequency and theremainder of communications occur at a second frequency. For example, RFprobe 120 may transmit RF energy at 5.8 GHz, and passive tag 120 mayscavenge power at the same frequency. In this example, the remainder ofthe communications may occur at 2.4 GHz. In other embodiments, powertransfer and communications occur at the same frequency. For example,power transfer and data communications may all occur at 5.8 GHz. Anyfrequency may be used for power transfer and/or data communicationswithout departing from the scope of the present invention.

In some embodiments, the RF signal used for power transfer remains onduring an entire time that the RF probe and the tag are communicating.For example, the RF probe may transmit a RF signal to power the tagwhile also transmitting an RF signal that has a clock signal and/or datasignal modulated thereon. In other embodiments, the RF signal used forpower transfer is turned off when data transfer takes place. Forexample, the RF probe may transmit the RF signal used for power transferfor a period of time, and the the RF probe may stop transmitting the RFsignal used for power transfer and start transmitting RF signal(s) usedfor data transfer. These and other embodiments are more fully describedbelow with reference to the remaining figures.

FIG. 2 shows a top view and section view of a package that includes apassive tag. Top view 200 shows passive tag 140 embedded in package 130.Package 130 may be any type of package. For example, in someembodiments, package 130 encases a product 210, and the product is anitem being tracked using passive tag 140. The product within package 130may be an integrated circuit, and package 130 may be an integratedcircuit package such as a quad flat pack (QFP), or any other type ofpackage.

As shown in section A-A of FIG. 2, some embodiments include anindentation 132 in package 130 within which passive tag 140 is affixed.Passive tag 140 may be affixed to package 130 in any manner. Forexample, in some embodiments, passive tag 140 is embedded in an epoxylayer within indentation 132. Also for example, in some embodiments,passive tag 140 is embedded within the package such that some of thepackage material is above the passive tag.

Passive tag 140 is small. In some embodiments, passive tag 140 is 100microns square. In other embodiments, passive tag 140 is larger than 100microns square, and in still further embodiments, passive tag 140 issmaller than 100 microns square. In some embodiments, passive tag 140 isa bare semiconductor die, and in other embodiments, passive tag 140 isenclosed within its own package.

The various elements of FIG. 2 are not shown to scale. Specifically, thesizes of passive tag 140 and indentation 132 are greatly exaggerated. Insome embodiments, package 130 is large enough to be handled by a humanhand, whereas passive tag 140 is barely visible to the human eye.

FIG. 3 shows a tip of an RF probe and a passive RF tag. RF probe 120includes a tip 122 that is smaller than the main body of the RF probe.In some embodiments, the tip 122 is substantially the same size aspassive tag 140. In other embodiments, tip 122 is larger than passivetag 140, and in still further embodiments, tip 122 is smaller thanpassive tag 140. RF probe 120, tip 122, and passive tag 140 are notdrawn to scale. For example, in some embodiments, RF probe is sized tobe comfortably held in a human hand, and passive tag 140 is small enoughso as to be barely visible to the human eye.

In operation, tip 122 is placed in the vicinity of passive tag 140, andRF energy emitted by the RF probe 120 is scavenged by passive tag 140 topower circuitry that is included in the passive tag. Data communicationbetween the RF probe and the passive tag may commence after the passivetag is powered. In some embodiments, both the RF probe and the passivetag include a first conductive coil for emitting (RF probe) andscavenging (passive tag) RF energy. Also in some embodiments, both theRF probe and the passive tag include additional coils used for otherpurposes. These embodiments and others are more fully described below.

FIG. 4 shows the tip of an RF probe and a passive RF tag, both withthree conductive coils affixed thereto. As used herein, the term“conductive coil” refers to at least one loop of conductive material,where each loop is referred to as a “turn.” Passive tag 140 is shownincluding three conductive coils, each with a plurality of turns.Passive tag 140 is shown having a footprint that corresponds to theoutermost rectangle. In some embodiments, coils 460, 470, and 480 areall within the footprint of passive tag 140, and in other embodiments, aportion of one or more coils is outside the footprint of the passive tag140.

Coils 460, 470, and 480 may be fabricated as part of passive tag, or maybe fabricated separately and then attached to passive tag 140. In eithercase, the coils are considered to be “affixed” to the passive tag. Insome embodiments, passive tag 140 is a semiconductor die, and one ormore of coils 460, 470, and 480 are formed in one or more metal layersof the semiconductor die. Any number of turns may be included in eachcoil without departing from the scope of the present invention.

RF probe tip 122 also includes multiple coils 410, 420, and 430. Asshown in FIG. 4, each coil in RF probe tip 122 corresponds to one coilin passive tag 140. For example, coil 410 corresponds to coil 460, coil420 corresponds to coil 470, and coil 430 corresponds to coil 480. Whenplaced in close proximity to each other, the corresponding coils becomeinductively coupled and can either transfer energy or communicate. Forexample, in some embodiments, RF probe 120 includes circuitry to drivecoil 410 with RF energy at a first frequency. When coils 410 and 460 areinductively coupled, currents are induced in coil 460 that allowcircuits electrically coupled to coil 460 to scavenge power. Also forexample, RF probe 120 may drive other signals, such as data, clock, or acarrier signal on coils 420 and 430, and passive tag 140 may receivethese signals when coil 470 is inductively coupled to coil 420, and coil480 is inductively coupled to coil 430.

The RF signal used to provide power, and the RF signal(s) used forcommunications may be at the same or different frequencies. For example,in some embodiments, Coil 410 is driven at 5.8 GHz to provide power topassive tag 140, and coils 420 and 430 are driven at 2.4 GHz. In otherembodiments, all coils are driven at 5.8 GHz or 2.4 GHz. In stillfurther embodiments, the coils are driven at frequencies other than 2.4GHz or 5.8 GHz.

FIG. 5 shows the tip of an RF probe and a passive RF tag, both with fourconductive coils affixed thereto. RF probe tip 122 is shown with coils510, 520, 530, and 540, and passive tag 140 is shown with coils 560,570, 580, and 590. When RF probe tip 122 and passive tag 140 are inclose proximity, coil 510 inductively couples with coil 560, coil 520inductively couples with coil 570, coil 530 couples with coil 580, andcoil 540 couples with coil 590.

In some embodiments, one coil pair is used to transfer power, and theremaining coil pairs are used for other purposes. For example, the coilpair 510, 560 may be used transfer power, coil pair 520, 570 may be usedfor bidirectional data transfer, coil pair 530, 580 may be used toprovide a clock signal from the RF probe to the passive tag, and coilpair 540, 590 may be used to provide a carrier signal from the RF probeto the passive tag.

The various coils in the RF probe inductively couple with thecorresponding coils in the passive tag when the coils are in closeproximity and they are sufficiently aligned. If the distance between thecoils is too great, or the alignment is too far off, the RF probe cannoteffectively communicate with the passive tag. In some embodiments, theRF probe and/or the package include alignment mechanisms to aid in thealignment of the coils in the RF probe tip with the coils in the passivetag. Various alignment mechanisms are described below with reference toFIGS. 6 and 7.

FIG. 6 shows a package with a notched indentation and a matching RFprobe. In embodiments represented by FIG. 6, the shape of theindentation 132 matches a shape of the RF probe 120 to aid in alignment.For example, indentation 132 includes notch 610, and RF probe tip 122includes protrusion 620, where the shape of the protrusion 620 matcheswith the shape of notch 610.

FIG. 7 shows a package with a trapezoidal indentation and a matching RFprobe. In embodiments represented by FIG. 7, RF probe 120 includes atrapezoidally shaped tip 122. Package 132 also includes a trapezoidallyshaped indentation 132 to facilitate alignment of RF probe 120 andpackage 130.

Notch 610 (FIG. 6) and the trapezoidal shape shown in FIG. 7 areexamples of surface features that match features on the RF probe tofacilitate alignment of conductive coils. Any surface feature of thepackage may be paired with any feature of the RF probe tip in orderfacilitate alignment of the coils without departing from the scope ofthe present invention. For example, in FIG. 6, the alignment surfacefeature includes a notch, and in FIG. 7, the alignment surface featureincludes a trapezoidal shape.

FIG. 8 shows a block diagram of a passive tag. Passive tag 140 includesdigital circuits 810, sensors 820, and RF circuits 830. Digital circuits810 include program ROM, Cryptographic functions (Crypto), one-timeprogrammable (OTP) device(s), and control circuitry (Control). TheProgram ROM stores hardcoded program logic that cannot be modified. TheOTP stores information that is used to uniquely identify the passivetag. For example, the OTP may store encryption keys and/or chip serialnumber. In some embodiments, the OTP cells are pre-provisioned duringmanufacture or test of the passive tag. In some embodiments, the OTPincludes a contact pad interface that allows fuses to be blown, but thatdoes not allow reads. In some embodiments, the contact pad interface isremoved from the circuit by blowing fuses after the OTP cells areprogrammed.

The cryptographic function may perform any type of cryptography. Forexample, in some embodiments, the cryptographic function performs256-bit AES cryptography. In other embodiments, the cryptographicfunction performs an asymmetric cryptographic algorithm.

Digital circuits 810 may include any type of control function. Forexample, in some embodiments, digital circuits 810 include state machinelogic that manages the execution of the Program ROM as well as managingcontrol interfacing between the analog and the digital sub-modules.

Sensors 820 includes startup and power circuits and threat detectioncircuits. The startup and power sensors may be used to determine theright time to power the digital circuits as well as managing powercoupling signaling to the RF probe.

The threat detection sensors may detect any type of catastrophic threatand disable the passive tag. For example, in some embodiments, thethreat detection sensors include mechanical sensing that results indestruction of the passive tag when tampered with.

RF circuits 830 includes energy conditioning & storage, input/output(I/O) circuitry, a conductive coil for power coupling, and one or moreadditional conductive coils for I/O. In some embodiments, energyconditioning and storage performs rectification and filtering. Forexample, some embodiments power the digital circuits with a DC powersource. In these embodiments, energy conditioning and storage rectifiesthe RF energy received on the conductive coil for power coupling, andprovides a DC power source to other circuitry. In other embodiments, thedigital circuits are adiabatic circuits that utilize the RF signal as apower source directly. Energy storage may be in the form of capacitancein the semiconductor die. Although the amount of energy storage may besmall, the power requirements of the passive tag are also small.

The I/O circuitry is electrically coupled to the I/O coils. In someembodiments, the I/O circuitry modulates outgoing data onto carriersignals and demodulates data from carrier signals. The I/O circuitry mayalso demodulate a clock signal or condition a received carrier signal.Examples of I/O circuitry are discussed below with reference to FIGS.9-14.

The coil for power coupling and the I/O coils are conductive coils withat least one turn. The coil for power coupling is electrically coupledto the energy conditioning and storage, and the I/O coils areelectrically coupled to the I/O circuitry. In some embodiments, each I/Ocoil has a single dedicated purpose, and in other embodiments, one ormore of the I/O coils have a shared purpose. For example, a single I/Ocoil may be dedicated to an incoming data signal, outgoing data signal,an incoming clock signal, or an incoming carrier signal. Also forexample, a single I/O coil may be shared for two or more of incoming oroutgoing data, incoming clock, or incoming carrier signal. Example coilsare shown FIGS. 4, 5, and 9-14.

FIGS. 9-13 show block diagrams of RF sections of passive tags inaccordance with various embodiments of the present invention. FIG. 9shows three conductive coils 460, 470, 480, corresponding to theconductive coils shown in FIG. 4. Conductive coil 460 is used forscavenging RF power, conductive coil 470 is used for bidirectional datacommunications, and conductive coil 480 is used to receive a carriersignal transmitted by the RF probe.

In embodiments represented by FIG. 9, RF section 830 includes tuningcircuits 904, 914, and 924, rectification circuit 906, data and clockdemodulation circuit 916, and data modulation circuit 918. In operation,conductive coil 460 is coupled to tuning circuit 904 to tune the coil toreceive RF energy at a first frequency (F1) transmitted by an RF probe.Tuning circuit 904 (and all tuning circuits shown in the variousfigures) may include any components in any configuration useful fortuning conductive coil 460. For example, tuning circuit 904 may includeparallel or series connected reactive elements. The received RF signalis rectified by circuit 906, and filtered by decoupling capacitor 908 toproduce a direct current (DC) voltage (VDD) to power other circuitswithin the passive tag. For example, VDD may be used to power othercircuits within RF section 830, as well as digital circuits (810, FIG.8) within the passive tag.

Conductive coil 480 is electrically coupled to tuning circuit 924. Thecombination of coil 480 and tuning circuit 924 are tuned to receive acarrier signal at a second frequency (F2). In embodiments represented byFIG. 9, an RF probe transmits a carrier signal at F2 using a conductivecoil that is paired to conductive coil 480. For example, RF probe 120(FIG. 3) may transmit a carrier signal at F2 using conductive coil 430(FIG. 4). The carrier signal at F2 is received by the passive tag andprovided to other RF circuits within RF section 830.

Coil 470 is electrically coupled to tuning circuit 914, which is in turnelectrically coupled to data and clock demodulation circuit 916 and datamodulation circuit 918. Data and clock demodulation circuit 916 receivesa modulated carrier signal at frequency F2, and demodulate the data andclock signals. Any suitable type of modulation may be employed and anycorresponding type of frequency translation and demodulation circuitrymay be included within circuits 916. In some embodiments, the data andclock signals are at KHz rates. For example, data rates may be about 10KHz, whereas the carrier signal upon which the data is modulated may beat a few GHz.

Coil 470 and tuning circuit 914 are also electrically coupled to datamodulation circuit 918. In some embodiments, data modulation circuit 918communicates the data to the RF probe by modulating the impedance ofcoil 470. When the RF probe is transmitting an RF carrier, and coil 470is inductively coupled to a coil on the RF probe, the RF probe can sensethe impedance modulation and receive the data.

The combination of data and clock demodulation circuit 916 and datamodulation circuit 918 form a data input/output circuit that iselectrically coupled to coil 470. This combination, along with coil 470,is used for half duplex bidirectional data. Data is received when amodulated carrier is received, and data is transmitted when theimpedance of coil 470 is modulated.

FIG. 10 shows three conductive coils 460, 470, 480, corresponding to theconductive coils shown in FIG. 4. Conductive coil 460 is used forscavenging RF power, conductive coil 470 is used for bidirectional datacommunications, and conductive coil 480 is used to demodulate a clocksignal and to receive a carrier signal transmitted by the RF probe.

In embodiments represented by FIG. 10, RF section 830 includes tuningcircuits 904, 914, and 924, rectification circuit 906, data demodulationcircuit 1016, and data modulation circuit 918. In operation, conductivecoil 460 is coupled to tuning circuit 904 to tune the coil to receive RFenergy at a frequency (F2) transmitted by an RF probe. Tuning circuit904 (and all tuning circuits shown in the various figures) may includeany components in any configuration useful for tuning conductive coil460. For example, tuning circuit 904 may include parallel or seriesconnected reactive elements. The received RF signal is rectified bycircuit 906, and filtered by decoupling capacitor 908 to produce adirect current (DC) voltage (VDD) to power other circuits within thepassive tag. For example, VDD may be used to power other circuits withinRF section 830, as well as digital circuits (810, FIG. 8) within thepassive tag.

Conductive coil 480 is electrically coupled to tuning circuit 924. Thecombination of coil 480 and tuning circuit 924 are tuned to receive amodulated carrier signal at the same frequency (F2) used to transferpower. In embodiments represented by FIG. 10, an RF probe transmits amodulated carrier signal at F2 using a conductive coil that is paired toconductive coil 480. For example, RF probe 120 (FIG. 3) may transmit amodulated carrier signal at F2 using conductive coil 430 (FIG. 4).

In embodiments represented by FIG. 10, the carrier signal received byconductive coil 480 is modulated with a clock signal. Clock demodulationcircuit 1024 demodulates a clock signal and also filters the incoming RFsignal to recover the carrier signal at F2. The carrier signal at F2 isprovided to other RF circuits within RF section 830.

Coil 470 is electrically coupled to tuning circuit 914, which is in turnelectrically coupled to data demodulation circuit 1016 and datamodulation circuit 918. Data demodulation circuit 1016 receives amodulated carrier signal at frequency F2, and demodulate the datasignal. Any suitable type of modulation may be employed and anycorresponding type of frequency translation and demodulation circuitrymay be included within circuits 1016. In some embodiments, the datasignal is at KHz rates. For example, data rates may be about 10 KHz,whereas the carrier signal upon which the data is modulated may be at afew GHz.

Coil 470 and tuning circuit 914 are also electrically coupled to datamodulation circuit 918. In some embodiments, data modulation circuit 918communicates the data to the RF probe by modulating the impedance ofcoil 470. When the RF probe is transmitting an RF carrier, and coil 470is inductively coupled to a coil on the RF probe, the RF probe can sensethe impedance modulation and receive the data.

The combination of data demodulation circuit 1016 and data modulationcircuit 918 form a data input/output circuit that is electricallycoupled to coil 470. This combination, along with coil 470, is used forhalf duplex bidirectional data. Data is received when a modulatedcarrier is received, and data is transmitted when the impedance of coil470 is modulated.

FIG. 11 shows three conductive coils 460, 470, 480, corresponding to theconductive coils shown in FIG. 4. Conductive coil 460 is used forscavenging RF power, conductive coil 470 is used for clock, carrier, anddata reception, and conductive coil 480 is used for data transmission.

In embodiments represented by FIG. 11, RF section 830 includes tuningcircuits 904, 914, and 924, rectification circuit 906, clockdemodulation circuit 1024, data demodulation circuit 1016, and datamodulation circuit 918. In operation, conductive coil 460 is coupled totuning circuit 904 to tune the coil to receive RF energy at a frequency(F2) transmitted by an RF probe. Tuning circuit 904 (and all tuningcircuits shown in the various figures) may include any components in anyconfiguration useful for tuning conductive coil 460. For example, tuningcircuit 904 may include parallel or series connected reactive elements.The received RF signal is rectified by circuit 906, and filtered bydecoupling capacitor 908 to produce a direct current (DC) voltage (VDD)to power other circuits within the passive tag. For example, VDD may beused to power other circuits within RF section 830, as well as digitalcircuits (810, FIG. 8) within the passive tag.

Conductive coil 470 is electrically coupled to tuning circuit 914. Thecombination of coil 470 and tuning circuit 914 are tuned to receive amodulated carrier signal at the same frequency (F2) used to transferpower. In embodiments represented by FIG. 11, an RF probe transmits amodulated carrier signal at F2 using a conductive coil that is paired toconductive coil 470. For example, RF probe 120 (FIG. 3) may transmit amodulated carrier signal at F2 using conductive coil 230 (FIG. 4).

In embodiments represented by FIG. 11, the carrier signal received byconductive coil 470 is modulated with clock and data signals. Clockdemodulation circuit 1024 demodulates a clock signal and also filtersthe incoming RF signal to recover the carrier signal at F2. The carriersignal at F2 is provided to other RF circuits within RF section 830.

Coil 470 and tuning circuit 914 are also electrically coupled to datademodulation circuit 1016. Data demodulation circuit 1016 receives amodulated carrier signal at frequency F2, and demodulate the datasignal. Any suitable type of modulation may be employed and anycorresponding type of frequency translation and demodulation circuitrymay be included within circuits 1016. In some embodiments, the datasignal is at KHz rates. For example, data rates may be about 10 KHz,whereas the carrier signal upon which the data is modulated may be at afew GHz.

Conductive coil 480 is electrically coupled to tuning circuit 924, whichis in turn coupled to data modulation circuit 918. In some embodiments,data modulation circuit 918 communicates the data to the RF probe bymodulating the impedance of coil 480. When the RF probe is transmittingan RF carrier, and coil 470 is inductively coupled to a coil on the RFprobe, the RF probe can sense the impedance modulation and receive thedata. In other embodiments, data modulation circuit 918 communicates thedata to the RF probe by modulating and transmitting a carrier at F2.

FIG. 12 shows three conductive coils 460, 470, 480, corresponding to theconductive coils shown in FIG. 4. Conductive coil 460 is used forscavenging RF power, conductive coil 470 is used for clock and carrierreception and data transmission, and conductive coil 480 is used fordata reception.

In embodiments represented by FIG. 12, RF section 830 includes tuningcircuits 904, 914, and 924, rectification circuit 906, clockdemodulation circuit 1024, data demodulation circuit 1016, and datamodulation circuit 918. In operation, conductive coil 460 is coupled totuning circuit 904 to tune the coil to receive RF energy at a frequency(F2) transmitted by an RF probe. Tuning circuit 904 (and all tuningcircuits shown in the various figures) may include any components in anyconfiguration useful for tuning conductive coil 460. For example, tuningcircuit 904 may include parallel or series connected reactive elements.The received RF signal is rectified by circuit 906, and filtered bydecoupling capacitor 908 to produce a direct current (DC) voltage (VDD)to power other circuits within the passive tag. For example, VDD may beused to power other circuits within RF section 830, as well as digitalcircuits (810, FIG. 8) within the passive tag.

Conductive coil 470 is electrically coupled to tuning circuit 914. Thecombination of coil 470 and tuning circuit 914 are tuned to receive amodulated carrier signal at the same frequency (F2) used to transferpower. In embodiments represented by FIG. 11, an RF probe transmits amodulated carrier signal at F2 using a conductive coil that is paired toconductive coil 470. For example, RF probe 120 (FIG. 3) may transmit amodulated carrier signal at F2 using conductive coil 230 (FIG. 4).

In embodiments represented by FIG. 12, the carrier signal received byconductive coil 470 is modulated with a clock signal. Clock demodulationcircuit 1024 demodulates a clock signal and also filters the incoming RFsignal to recover the carrier signal at F2. The carrier signal at F2 isprovided to other RF circuits within RF section 830.

Coil 470 and tuning circuit 914 are also electrically coupled to datamodulation circuit 918. In some embodiments, data modulation circuit 918communicates the data to the RF probe by modulating the impedance ofcoil 470. When the RF probe is transmitting an RF carrier, and coil 470is inductively coupled to a coil on the RF probe, the RF probe can sensethe impedance modulation and receive the data.

Coil 480 and tuning circuit 924 are electrically coupled to datademodulation circuit 1016. Data demodulation circuit 1016 receives amodulated carrier signal at frequency F2, and demodulate the datasignal. Any suitable type of modulation may be employed and anycorresponding type of frequency translation and demodulation circuitrymay be included within circuits 1016. In some embodiments, the datasignal is at KHz rates. For example, data rates may be about 10 KHz,whereas the carrier signal upon which the data is modulated may be at afew GHz.

FIG. 13 shows an RF section of a passive tag that includes fourconductive coils. The first conductive coil is used for RF powertransfer as described above. For example, any of the RF power transfermechanisms described above with reference to FIGS. 9-12 may be includedin embodiments represented by FIG. 13. The RF power transfer circuitsand the corresponding conductive coil are not shown in FIG. 13. FIG. 13does show conductive coils 570, 580, and 590. These conductive coils arealso described with reference to FIG. 5.

Data demodulation circuit 1016, data modulation circuit 918, and tuningcircuit 914 are electrically coupled to conductive coil 570. Thesecircuits and their operation are described above. Tuning circuit 924 iselectrically coupled to conductive coil 590, and receives a carrier atfrequency (F2). This is also described above.

Clock demodulation circuit 1310 is electrically coupled to conductivecoil 580 and tuning circuit 924. In operation, clock demodulationcircuit 1310 receives a modulated carrier, and demodulates a clocksignal.

In embodiments represented by FIG. 13, four separate conductive coilsare included on a passive tag. One is used for RF power transfer, asecond is used for bidirectional data communications, a third is usedfor a clock signal, and a fourth is used to transmit a carrier.

FIG. 14 shows a block diagram of a passive RF tag with adiabaticcircuits. Embodiments represented by FIG. 14 differ from the previouslydescribed embodiments in that the power conditioning does not includerectification. Instead, the RF power that is scavenged is used directlyas a power source for adiabatic digital circuits. For example, as shownin FIG. 14, alternating current (AC) power is supplied directly from theRF power received from the combination of conductive coil 460 and tuningcircuit 904.

Adiabatic digital circuits 1410 receive a data signal provided by tuningand extraction circuit 1402, which is in turn electrically coupled toconductive coil 470. Adiabatic digital circuits 1420 provide data totuning and modulation circuit 1412, which is in turn coupled toconductive coil 480.

Adiabatic circuits 1410 and 1420 represent digital circuits within apassive tag such as digital circuits 810 (FIG. 8). Adiabatic circuitsare good candidates for the digital circuits in passive tag 140 in partbecause the power transfer is already an AC signal, data rates arerelatively low, and the power consumption is also very low.

FIG. 15 shows a flowchart of methods in accordance with variousembodiments of the present invention. In some embodiments, method 1500is performed by a passive tag in accordance with various embodiments ofthe present invention. The various actions in method 1500 may beperformed in the order presented, in a different order, orsimultaneously. Further, in some embodiments, some actions listed inFIG. 15 are omitted from method 1500.

Method 1500 begins at 1510 in which RF energy is received at a firstfrequency from a first conductive coil having a plurality of turns. Insome embodiments, the first conductive coil corresponds to coil 460 asshown in the previous figures. At 1520, the RF energy is conditioned topower digital circuits. In some embodiments, this corresponds torectifying and filtering the RF energy to produce a DC power supplyvoltage suitable to power digital circuits.

At 1530, data is transmitted using a second conductive coil having aplurality of turns when reception of the RF energy from the first coilstops. In some embodiments, this corresponds to sensors 820 (FIG. 8)detecting that the RF energy is no longer being transmitted by an RFprobe. For example, referring to FIG. 11, data may be transmitted usingdata modulation circuitry 918 when RF energy is no longer being receivedat conductive coil 460. The RF energy and the modulated data carrier maybe at the same frequency (F2), or may be at different frequencies (F1),(F2).

FIG. 16 shows a flowchart of methods in accordance with variousembodiments of the present invention. In some embodiments, method 1600is performed by a passive tag in accordance with various embodiments ofthe present invention. The various actions in method 1600 may beperformed in the order presented, in a different order, orsimultaneously. Further, in some embodiments, some actions listed inFIG. 16 are omitted from method 1600.

Method 1600 begins at 1610 in which RF energy is received at a firstfrequency from a first conductive coil having a plurality of turns. Insome embodiments, the first conductive coil corresponds to coil 460 asshown in the previous figures. At 1620, the RF energy is conditioned topower digital circuits. In some embodiments, this corresponds torectifying and filtering the RF energy to produce a DC power supplyvoltage suitable to power digital circuits.

At 1630, data is received using a second conductive coil having aplurality of turns when reception of the RF energy from the first coilstops. In some embodiments, this corresponds to sensors 820 (FIG. 8)detecting that the RF energy is no longer being transmitted by an RFprobe. For example, referring to FIG. 12, data may be received usingdata demodulation circuitry 1016 when RF energy is no longer beingreceived at conductive coil 460. The RF energy and the modulated datacarrier may be at the same frequency (F2), or may be at differentfrequencies (F1), (F2).

FIG. 17 shows a flowchart of methods in accordance with variousembodiments of the present invention. In some embodiments, method 1700is performed by an RF probe when communicating with a passive tag inaccordance with various embodiments of the present invention. Thevarious actions in method 1700 may be performed in the order presented,in a different order, or simultaneously. Further, in some embodiments,some actions listed in FIG. 17 are omitted from method 1700.

Method 1700 begins at 1710 in which an RF signal is transmitted at afirst frequency from a first conductive coil having a plurality of turnsto provide power to a passive tag. In some embodiments, this correspondsto an RF probe transmitting RF energy using conductive coil 410 (FIG.4), which is inductively coupled to conductive coil 460 as shown in theprevious figures. At 1720, the transmission of the RF signal is stopped.In some embodiments, the transmission of the RF signal is stopped afterit has been transmitted for a time period long enough to power thepassive tag.

At 1730, the RF probe communicates with the passive tag using a signalat a second frequency transmitted from a second conductive coil having aplurality of turns. In some embodiments, this corresponds to an RF probetransmitting a modulated carrier signal using conductive coil 420 (FIG.4) which is inductively coupled to conductive coil 470 on the passivetag. Communications may be half-duplex when the input data and outputdata share a single conductive coil, or may be full-duplex when theinput data and output data use separate conductive coils.

Although the present invention has been described in conjunction withcertain embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the scope of theinvention as those skilled in the art readily understand. It is to beclearly understood that the above description is made only by way ofexample, and not as a limitation on the scope of the invention.

What is claimed is:
 1. A method of operating a passive integratedcircuit comprising: receiving radio frequency (RF) energy at a firstfrequency from a first conductive coil having a plurality of turnsaffixed to the integrated circuit; conditioning the radio frequencyenergy to power digital circuitry in the passive integrated circuit; andtransmitting data using a second conductive coil having a plurality ofturns affixed to the integrated circuit when reception of radiofrequency energy at the first frequency from the first conductive coilhas stopped.
 2. The method of claim 1 wherein transmitting datacomprises modulating an impedance presented to the second conductivecoil when the second conductive coil is in the presence of a carriersignal at a second frequency.
 3. The method of claim 2 wherein the firstand second frequencies are the same.
 4. The method of claim 2 whereinthe first and second frequencies are different.
 5. The method of claim 1further comprising receiving a carrier signal at a second frequency on athird conductive coil having a plurality of turns affixed to theintegrated circuit.
 6. The method of claim 1 further comprisingreceiving an RF clock signal at a second frequency on a third conductivecoil having a plurality of turns affixed to the integrated circuit. 7.The method of claim 6 further comprising receiving a carrier signal at asecond frequency on a fourth conductive coil having a plurality of turnsaffixed to the integrated circuit.
 8. A method of operating a passiveintegrated circuit comprising: receiving radio frequency energy at afirst frequency from a first conductive coil having a plurality of turnsaffixed to the integrated circuit; conditioning the radio frequencyenergy to power digital circuitry in the passive integrated circuit; andreceiving data using a second conductive coil having a plurality ofturns affixed to the integrated circuit when reception of radiofrequency energy at the first frequency from the first conductive coilhas stopped.
 9. The method of claim 8 wherein receiving data comprisesdemodulating digital data from a carrier signal at a second frequency.10. The method of claim 9 wherein the first and second frequencies arethe same.
 11. The method of claim 9 wherein the first and secondfrequencies are different.
 12. The method of claim 8 further comprisingreceiving a carrier signal at a second frequency on a third conductivecoil having a plurality of turns affixed to the integrated circuit. 13.The method of claim 8 further comprising receiving an RF clock signal ata second frequency on a third conductive coil having a plurality ofturns affixed to the integrated circuit.
 14. The method of claim 13further comprising receiving a carrier signal at a second frequency on afourth conductive coil having a plurality of turns affixed to theintegrated circuit.
 15. A method of operating a radio frequency (RF)probe to communicate with a passive tag, the method comprising:transmitting a signal at a first frequency using a first conductive coilwith a plurality of turns to provide a source of power to the passivetag; stopping the transmission of the signal at the first frequency; andcommunicating with the passive tag using a signal at a second frequencytransmitted from a second conductive coil with a plurality of turns. 16.The method of claim 15 wherein the first and second frequencies are thesame.
 17. The method of claim 15 wherein the first and secondfrequencies are different.
 18. The method of claim 15 whereincommunicating with the passive tag comprises modulating digital dataonto a carrier signal at the second frequency.
 19. The method of claim15 wherein communicating with the passive tag comprises sensingimpedance changes present in a field near the second conductive coil.